Welding machine and procedure



Feb. 1, 1966 o. w. GARVER ETAL 3,233,072

WELDING MACHINE AND PROCEDURE Filed March 15, 1962 9 Sheets-Sheet 2 mOscar- @Af. Carver hf'recievidg 6. UHmqm Christian. Q4 6mm? ym w M ppFeb. 1, 1966 o. w. GARVER ETAL WELDING MACHINE AND PROCEDURE 9Sheets-Sheet 4 Filed March 15, 1962 503 SCI 2 ch risfi'an 522m.

Feb. 1, 1966 o. w. GARVER ETAL 3,233,072

WELDING MACHINE AND PROCEDURE 9 Sheets-Sheet 5 Filed March 15, 1962 T. fJw m Y 2 G wnawm mawamw 56% w 7 3% xi $2M M mmm m nI/III/II.

Feb. 1, 1966 o. w. GARVER ETAL 3,233,072

WELDING MACHINE AND PROCEDURE 9 Sheets-Sheet 6 Filed March 15, 1962NVSMTOCLU m m Wm M ww w q 260% a? in; Em

Feb. 1, 1966 o. w. GARVER ETAL 3,233,072

WELDING MACHINE AND PROCEDURE Filed March 15, 1962 9 Sheets-Sheet '7Feb. 1, 1966 o. w. GARVER ETAL 3,233,072

WELDING MAGHINE AND PROCEDURE WELD A @T 3% E 331 F5 AR TEST 585 SW J 537480 460 g coum I ZERO RESET COUNTER sw g W Filed March 15, 1962 9Sheets-Sheet 8 Z r I COUNTER 5w I MAIN MOTOR l 598 l ORIENT DRIVE MOTORHOPPER COARSE ORIENT MOTORS (2) l 56% q 54,: 3! I CLUTCH 562 M75 Z 94 ifAKE i :70 $.49! I EAR 0R0 E RELOADP 55 Lmmflj EARDR i 0? 534 RELEASE I l535 455 4 g 3l4- i I I 1 l UP 539 J F M A a gggm ENT DOWN f R 5|o0N"T|ME OF CAM swn'cu SECTIONS I INVENTORS 05cm W. GARVER FREDERICK E.ULLMAN fiamsna u STETTLER ANS OPP 1= :W ,MM,1M0M

ATTYS.

United States Patent 3,233,072 WELDING MACHINE AND PROCEDURE Oscar W.Garver, Villa Park, Frederick E. Ullman, Winnetka, Christian H.Stettler, Northbrook, and Hans W. Kopp, Evanston, Ill., assignors toGrotnes Machine Works, Inc., Chicago, 11]., a corporation of IllinoisFiled Mar. 15, 1962, Ser. No. 180,415 7 Claims. (Cl. 219-93) The presentinvention relates to welding machines and procedures and moreparticularly to machines for welding ears to pails or the like.

I11 the manufacture of metal shipping pails, it is conventional to weldears or projections to the sides of the pail for receiving the ends of awire bail. The ear may be in the form of a cup-shaped stamping having acentral opening for the bail and having lateral projections which seatagainst the side of the pail. Since the pails are commonly made of sheetsteel, it is desirable to protect or decorate the outer surface eitherby painting or by lithographing which, in addition to providing physicalprotection, often serves to identify the contents, to provide acolorful, attractive appearance, and to carry an advertising message. Itis desirable that the painted or lithographed coating be applied to theside of the pail while it is still flat, prior to Welding. Moreover, itis desirable that the coating be continuous, covering all of the surfacearea. This requires that the bail ears be secured after the coating hasbeen applied, so that any spot welding of the ears must take placethrough the coating. Efforts have been made in the past to weld an earor other attachment to a painted surface by forming, on the attachment,a sharp projection so that when pressure is applied, the projectionestablishes electrical contact to permit flow of welding current.However, it has not been possible to weld through an insulating coatingwith one hundred percent reliability. Consequently, use of thisprocedure has been limited to containers having thin walls and where thestrength of the weld has not been an important factor, for example, inthe welding of a key to the lid of a coffee can. One difficulty whichhas been experienced in this type of welding is the flashing which takesplace when the initial electrical contact is made between the sharpprojection and the base resulting in overheating and destruction of theprojection, with inability to complete the weld.

Welding through an insulating coating has been avoided in the case ofshipping pails because of inability to make a consistent weld, becauseof the high degree of strength required in the weld, particularly whenthe pail is to be filled with a dense, heavy substance, and theinability to properly inspect the weld for soundness.

It is, accordingly, an object of the present invention to provide animproved welding machine capable of spot Welding a sheet metalattachment to a coated and insulated base member. More specifically, itis an object to provide a machine for spot welding bail ears to thesides of a shipping pail where the entire outer surface has beenprepainted or lithographed. It is a related object to provide a machinefor welding bail ears to a coated and insulated surface even though thecoating may be formed of a tough material diiiicult to penetrate andregardless of the thickness of the coat. It is another object to providea machine for welding a bail ear to a coated container which produces aweld having exceptional strength, equal in all respects to that obtainedwhen welding to an uncoated surface and distinguished by a well definednugget which is free of contamination by the coating material or thedecomposition products of the coating material.

It is a more specific object to provide a welding projeccedure andmachine which makes use of a sharp projection formed on the attachmentto be welded but which 3,233,072 Patented Feb. 1, 1966 completely avoidsthe problem of fiashaway, i.e., the destruction of the projection byviolent overheating when initial contact is made between the projectionand the base metal.

It is another object to provide a procedure in machines for spot weldingof bail ears on a shipping bail which is not limited to a particulartype of pail but which may be easily and quickly adjusted for use withpails of different size and different thickness having beadconfigurations and with ears of widely differing construction. It is afurther object of the present invention to provide a welding procedurewhich is not limited to use with thin metals of the type employed inlight shipping containers but which may be used where the metalthickness varies over wide limits with full utilization of the strengthof the attached parts. In this connection, it is an object to provideprocedure and apparatus for welding a sheet metal attachment to anycoated base member, for example, in the automotive field where it may bedesired to secure a metal part to the body of an automobile afterdipping in rustproofing or protective coating material.

It is yet another object of the present invention to provide a weldingmachine which is not only capable of producing a reliable weld but whichis extremely rapid, a single machine being capable of processingshipping pails at the rate of 2400 units per hour or even higher.

It is yet another object to provide a machine of the above type which iswell suited for heavy industrial use, which may be operated for longperiods of time without maintenance or adjustment and which issubstantially foolproof, permitting safe operation on a high productionbasis even with unskilled or inexperienced personnel.

Other objects and advantages of the invention will become apparent uponreading the attached detailed description and upon reference to thedrawings, in which:

FIGURE 1 shows a shipping pail with a bail ear affixed by the presentmachine;

FIG. 1a is an enlarged perspective showing one of the ears;

FIG. 2 is a front elevation of an ear welding machine constructed inaccordance with the present invention somewhat simplified for easyunderstanding;

FIG. 3 is a left-hand elevation of the machine shown in FIG. 2;

FIG. 4 is a diagram showing the linkage for driving the positioningmembers;

FIG. 5 is a fragmentary front view of the machine showing the cams fordriving the transfer and positioning members.

FIG. 6 is a fragmentary perspective showing the ear escapement;

FIG. 7 is a fragmentary section taken along the line 7-7 in FIG. 6;

FIG. 8 is a fragmentary face view in partial section showing the pailorienting mechanism;

FIG. 9 is a fragmentary section taken along line 9-9 in FIG. 8 showingthe first seam detector;

FIG. 10 is a fragmentary section taken along the line 10-10 in FIG. 8showing the seam detector switch;

FIG. 11 is a fragmentary top view of the star wheel employed in thefirst seam detector;

FIG. 12 is a fragmentary section taken along the line 1212 in FIG. 8 andshowing the final seam detecting element;

FIG. 13 is a section taken along the line 13-13 in FIG. 2 showing themeans for moving the welding electrodes;

FIG. 14 is a fragmentary section taken along the line 1414 in FIG. 13showing the electrode advancing means in plan view;

FIG. 15 is a fragmentary section taken along the line 15.-15 in FIG. 13showing the electrodes in welding position;

FIG. 16 is an enlarged fragment showing the function of the centeringpin and supporting table; H l I .FIG. 17 is a vertical-sectiontakenalong line 17-17 in FIG. 14 showing theopening of the gatesto admit the welding electrodes;

FIG. l8.is a perspective of oneof the gates;

.FIG. 19 is a sectiontaken ontheline 1919 of FIG. 2 showing the earcheckingarm; i I

FIG. 20 is a view similar to FIG. 19 with the parts in amoved position;

1 1G 21 is a simplified schematic diagram of the control circuit; r

FIG. 22 is a plotlshowing the variation in applied, force,projectionheight and cur-rent as a function of time; and,

FlGS. 23a-23 e are enlarged sections of a typical weld at successivepoints" in thewelding cycle keyedto FIG. 22.

P While" the invention has been described in connection withapreferredembodiment, it will bennder-stood that We do not intend toli-rnit the. invention to the embodiment shown but intend, on thecontrary, to cover the various alternatives andfequivalent constructionsincluded within the spirit and scope of; the appended claims.

Turning now to FIG. 1 there is shown, inverted, a

shipping pail 30 of well-kiiown type having a top curl 31,

a bottom flange32 and -a seam 3.3. Located on opposite sides of the pailare bail ears 34, only one of which is visible in the figure, Themachine to be described is primarily intended for welding such ears inplace upon a prepainted or p-relithographedpail .While the invention isnot limitedlto any particular form of bail ear, a preferred form of ear(FIG. 1a) includes a cupshaped centr'al portion 35 having a centralopening 36 for receiving the end of the bail and having tabs 37, 38 forspot welding to the wall of the pail. i I

The machine, generally indicated at 50, has a longitudinal frame 51supported on a base 52. Extending upwardly' at the rear of the frame arepillars 53, 4 which support a. superstructure 55 in adjusted verticalposition. Pails 31) enter the machine at the left from an externalconveyor and, as will be described, each pail successively occupiesaseries of work stations in which the pails are acted upon. In themachine described, them are a total of six work stations indicated, at 616 6, respectively, in

which the pails are first oriented, then welded and, finally,

tested. For the sake of versatility and for optional functions orspecialized purposes, two of the'stations, inthe present instancestations 63 and 66, are idle. It will be understood, however, that thepails pass through the machine at closely spaced sequence so that all ofthe stations at any given time havepails positionedtherein. V

While the various functions performed by thernachine are closelyintegrated it will, nevertheless, be convenient for easy understandingto discuss the functions of the machine under separate appropriatesubheadings.

Pail transfer and positioning mechanism In the illustrative apparatus, alongitudinal pail transfer member is provided which extends under all ofthe stations and which reciprocates back and forth through a unitstation-to-station distance for the purpose of engaging the presenteddownwardly facing'edges of the pails and for moving all of themsimultaneously to the next station. Cooperating with the transfer memberis a longitudinally extending positioning member having means for movingthe same vertically between a lowered inactive position, at which timethe pails are engaged by the transfer member, and an upraised activeposition in which the pails are firmly held clear of the transfer memberso that the latter is free to make a return stroke. Th'etransfer memberin the present instance is in the form of a 1ongitudinally extending bar70 mounted on rollers 73, '74 (FIG. 19) for endwise movement in themachine and havinga plurlaity of pail-engaging members or lugs 71 72secured to its upper edge. A pair of cams are employed for moving thetransfer member in opposite directions. Thus, as shown in FIG. 5, drivecams indicated at 81, 82, mounted on a.cam shaft 83 act upon a bellcrank 84 which is pivoted for rocking movementabout a shaftYSS. .Atitsupper end the oran'k'is connected to a link:8 6 which,'in turn, ispivoted to a bracket 87 clamped to the transfer member 79. For thepurpose of driving the cam shaft 83, a motor 90 is'usedhaving a speedreduction unit 91.

For the purpose of moving the pails upwardly and clear of the transfermember 70 into a position to be acted upon, a positioning member isprovided having spaced sections 101, 102 which'mov'e upwardly anddownwardly in unison. The positioning member is formed in twolongitudinal sections in order to permit separate vertical positioningof the pail in the welding station as will be discussed in detail.

In o'rder to provide a wide base for positioning purposes,,the. sections101, 102 have corresponding spaced sections 101a, 101k 102a and 102bwhich straddle the transfer member 70 as shown in FIG. 3. Means areprovided along the top edge of each section for engaging the lower edgeofthe pails. Such means may take the form of lugs 165 or my take theform of rollers in the orienting stations 61, 62 to be discussed. Tounderstand the means forbodily raising and lowering the positioningmember 100, it will be noted that cams 111, 112, mounted on shaft 83 anddisposed immediately behind the cams 81 and 82. previously discussed,act upon a cam follower in the form of a bell crank 114 having a shaft115, Connected to the outer end of the bell crank 114 is a push rod 115'which is pinned to an arm 117 secured to a longitudinally extendingrocker shaft which is journalled at its end in suitable bearings 121. Toconvert the rockingmovement of the rocker shaft 120 to vertical movementof the positioning member, the shaft is provided with lift arms alongits length having short links which are coupled to thesections of thepositioning member and with radius arms being provided to insure thatthe elevation is eq ualized. I Thus the shaft 120 has lift arms 126carrying short links which are connected at their upper ends to brackets127 on the section 1920. For the purpose of transmitting equal movementto the section 10217, the bell crank shaft 115 has an arm 114a whichdrives a push rod 116a pinned to an arm 117a on a rocker shaft 120awhich extends along the rear of the machine. The rocker shaft 120acorresponds to the rocker shaft 120 previously discussed. Toelevatesection 1 6% the pushing member of the rocker shaft 120:: hasarms 125a which act upon short links 126a which are connected at theirupper ends to brackets 127a along the underside of themember ltlZb.

It will be apparent, then, that when the cams rotate themembers 102a and1021) will be moved upwardly through equal distances. To insure that themembers are guided. in thi upward movement, pairs of swingable radiusarms 129 are provided for each of the sections, forming a parallelogramlinkage.

While the above structure sufiic-es for elevating the sections 192a,102b of the positioning member 100, it will be understood that similarstructure is employed for elevating the two sections 161a, ltllb andwith corresponding reference numerals being used where applicable.

Since cams 8'1, 92 which reciprocate the transfer member and the cams111, 112 which move the positioning member Vertically are offset inphase, it will be seen from FIG. 3 that the effect is to advance thepails simul taneou'sly step by step. Taking the first station 61 by wayof example, when the positioning member 100 is upraised, the lugs on thetransfer member are moved to the left to a position under the enteringpail. When such entering pail, indicated at 30a in FIG. 2, is lowered bythe positioning member, it seats on the lugs 71 and 72. The transfermember 70 then moves to the right until the pail is in the first station61 whereupon the transfer member momentarily comes to rest. Thepositioning member 100, as a result of the cams 111, 112 and the linkagejust described, moves vertically, lifting the pail clear of the transfermember and in position to be acted upon in the first station. Each ofthe other pail in the series is similarly advanced one step.

In order to feed a pail into the machine and to remove a pail havingwelded ears from the machine, conveyor chains are provided at both theinput and. output. Referring to the input end, a conveyor chain 140,which preferably consists of two parallel sections is trained aboutshafts 141, 142, the shaft 142 being preferably mounted on thepositioning member 100 for movement up and down therewith. For drivingthe conveyor chain 140, a drive chain 143 is provided which is driven bya second chain 144 coupled to the driving motor. A similar setup isemployed at the output, with a conveyor chain 150 being trained aboutshafts 151, 152 and driven by chains 153, 154.

Rotary orienting mechanism In order to insure proper pail orientation,means are provided at the first station 61 for rotating the pail atrelatively high speed to an approximate position of orientation asdetermined by a weld bead on the side of the pail and at the secondstation for rotating the pail at a substantially slower speed to achieveprecise orientation. In order to understand the mechanism foraccomplishing such two-step orientation, reference is made to FIGS. 2and 8-11 and the schematic control diagram FIG. 21. Mounted on thesuperstructure 55 and centered with respect to the stations 61, 62 arerotating mechanisms 161, 162. Attention will first be given to therotating mechanism 161. The mechanism 161 is mounted upon a downwardlyextending pedestal 163 carrying a cylindrical housing 164 at its lowerend. The housing 161 has an outer shell for an adjusting purpose whichwill become clear as the discussion proceeds. Centered within thepedestal 163 is an input drive shaft 165, and projecting downwardlytherefrom is a disc drive shaft 166. Coupled to the lower end of thedisc drive shaft 166 is a drive disc 170 having a layer of rubber orother friction material 171 on its under surface for engaging thepresented upper edge of a pail 30. Downward pressure is exerted upon thedisc 170 so that the disc seats firmly against the pail by means of aresilient connection 172 which is interposed between the drive shaft 166and the disc. The resilient connection 172 is preferably in the form ofa resilient spider, a construction well-known to those skilled in theart.

For the purpose of controlling rotation of the disc, a clutch 175 isinterposed between the input shaft 165 and the output shaft 166, and tobring the output shaft to a stop on the plate when the clutch isdisengaged, an electric brake 176 is provided. The combined clutch andbrake together form a commercially available unit. To supply rotativepower for the input shaft 165, to rotate the same at a speed ofapproximately 50 r.p.m., a reduction drive is provided which includes adrive motor 180, a right-angled step-down connection 181 having adownwardly extending output shaft 182. Mounted on the shaft 182 is aspur gear 183 which meshes with a spur gear 184 at the upper end of theshaft 165. In order to permit rotation of the pail under the urging ofthe drive disc 170, rollers 185, which may be made of nylon or the like,are mounted along the upper edge of the positioning member 100.

In order to detect the arrival of the pail seam at a predeterminedpoint, and to deenergize the clutch and energize the brake when thisoccurs, a detector is provided in the form of a sharp edged member whichis biased against the side of the pail and which operates 6 anassociated switch when the sharp edge is engaged by the seam. Turning toFIGS. 10 and 11 the detector element is in the form of a star wheel 190mounted upon a shaft 191 carrying a cam 192 at its upper end foroperating a switch 193. The shaft, as shown in FIG. 9,

is mounted in a carrier 195. For biasing the carrier in the direction ofthe pail, the carrier is mounted upon a lever 196 which is pivoted atits upper end 197 and which is engaged by a coil spring 198. Thus whilethe pail rotates, the star wheel 190 presents an edge 190a in the pathof movement of the seam 33 on the pail. It will be understood by oneskilled in the art that even where a flush-type seam is employed,nevertheless, there is a narrow rather sharply defined groove on thesurface of the pail capable of engagement by the star wheel. When theseam rotates to the position shown in FIG. 11, the point 190a of thestar wheel enters the seam groove causing the star wheel to step onestep in the counterclockwise direction. The cam 192 at the upper end ofthe star wheel shaft thereupon actuates the switch 193 which, throughthe control circuit to be described, serves to disengage the clutch andenergize the brake to bring the pail to a stop.

.Means are provided for retracting the seam detector to an upper,out-of-the-way position during station to station transfer and forlowering the detector when a pail is in the orienting station. Tounderstand the retracting means reference ismade to FIGS. 3, 8 and 9. Itwill be noted that the detector assembly is not rigidly secured to thehousing of the rotating mechanism, but, instead, is mounted upon avertical slide 210 which engages way surfaces 211 secured to the housingmember outside of the housing 161. For moving the slide 210 upwardly anddownwardly, a positioning collar 215 is provided which surrounds thepedestal 163 and which is slidable thereon. Formed in the lower portionof the collar 215 is an annular groove 216 which is engaged by a roller217 pinned to the slide 210. Thus, it will be apparent that when thecollar is raised, the slide 210, and the detector assembly secured toit, is also raised, this condition being illustrated in FIG. 9. For thepurpose of moving the collar 215 upwardly during each transfer cycle, alinkage is provided which is operated by the rocker shaft 120. Suchlinkage includes an arm 220 (FIG. 3) which is connected to a push rod221 operating a bell crank 222. Motion is transmitted from the bellcrank 222 to a second or intermediate bell crank 223 by a parallelogramlinkage made up of links 224, 225. Motion is transmitted from the bellcrank 223 to a final bell crank 226 which is rotatable about a shaft 227via a second parallelogram linkage made up of parallel links 228, 229.For the purpose of transmitting the rocking movement of the shaft 227 tothe collar 215, arms 231, 232 (FIG. 8) are secured to the shaft,carrying rollers 233, 234 at thier forward ends which ride is an annulargroove 235 at the upper end of the collar. Means are provided forcamming the detector radially outward away from the pail as it isupraised for the purpose of clearing the flange at the end of the pailand the drive disc which engages it. In FIG. 9 it will be noted that thespring biased arm 196 which carries the detector element has a roller240 which rides on the surface of the way 211 and acts as a camfollower. Thus, when the detector is drawn upwardly, the roller 240rides up on the way swinging the detector outwardly. Conversely, whenthe collar 215 is lowered the roller 240 reaches the lower end of theway 211- providing dropoff so that the spring 198 is effective to biasthe detector element against the side of the pail.

It will be apparent, then, that upon rotation of the rocker shaft in onedirection the detector will be moved downwardly and inwardly intocontact with the pail and, upon movement in the other direction, i.e.,during transfer, the detector will be moved outwardly and upwardly to anout-of-the-way position. Because 7 of the dual parallelogram linkagejustdescribed, it is possible to adjust the height of the superstructure 55to accommodate pails of different heights, Without necessity forre'adjustin'g the angling of the collar-actuating arms 231, 232iThe'superstructure adjusting means will be covered at a' later point.

For the purpose oflim'iting maximum rotation of the pail to less than180i, it will be' understoodthat a duplicate of assembly 190 having aswitch 2'44 is provided in adiarnet rically opposite position (see FIG;3). As will be observed in'tlie cdntrol diagram FIG. 21, operation ofthe switch'in either of the" detector assemblies suflices to terminaterotation of the pail. Stopping the pail at either' of two 180 positionis' permissible since the ears to be welded to'the pail'are fixedinsymmetrical 180 positio'nsl For the purpose of simultaneouslypositioning the detector assemblies 190, 19011, the associated wayelements are secured to an outer shell 245 of the clampingsc'rew 246serve toclamp the outer shell 245 and the two detector assemblies in anyposition depend.- ing'up'on the desired position of the bail ears.

The net effect ofthe' orienting mechanism in the first station 61 is toproduce approximate orientation of the pail, say, within one quarterinch of the desired position on the periphery. Such orientation isapproximate because of the relatively high speed of rotation of thedrive disc 170r'equired to bring about a rotation of up to 180 in theshort time that the pail is in the station. The degree of overtravelafter cutoff is to some extent dependent upon whether the pail has beenrotated to a'larg'e angle or a small angle prior to cut off.

Thus, means rotating at a substantially slower speed are provided in thesecond station in order to achieve final and exact positioning. Sincethe'orienting mechanism employed in the second station is a substantialduplicate of that in the first, except for the speed of rotation and theconstruction of the detector element, corresponding reference numeralshave been employed to identify corresponding parts with addition ofsubscript a. To achieve a slower speed, onthe order of 6 r.p.m., astep-down ratio has been employed in the gears 183a, 184a, a s'contrasted with the step-up ratio in the gears 183, 184 in the companionunit. With regard to the construction of the slow speed detector, theelement, indicated at 250 in FIG. 12, has a sharp detecting edge 251 andis mounted upon a parallelogram linkage which includes links 252, 253.The link 253' is connected to a vertically extending shaft 254' whichcontrols switches 255', 256. The switch 255 is so adjusted as to operateimmediately upon the sharp edge 251 being engaged by the seam whereasthe switch 256 is adjusted to operate only after a predetermined amountof overtravel. The effective spacing between the switches 255, 256determines the positional tolerance, i.e., as long as the orientation iswithin prescribed limits, an ear will be welded to the pail. However,and as covered in the latter section, in the event that the switch 256is operated, indicating that the tolerance is exceeded, provision ismade for preventing a weld so that the pail may be removed from theproduction line and inserted again at the input side of the machine.Moreover, means are provided for registering the number of successivepails which are outside of the tolerance, i.e., without ears, and forsounding an alarm or shutting off the machine when a predeterminednumber has been exceeded, all as later covered in detail.

Using the above construction, with approximate and exact orientation insuccessive stations, orientation may be achieved within a peripheraltolerance on the order of 0.080 inch consistently and at high speed.Upon subsequent lowering of the pail by the positioning member, the pailis advanced into the next station 63. Thi station, in the presentconstruction, is an idle one in that no operation is performed upon thepail. However, this station contributes to the versality of the machinein that any desired operation, requiring an oriented pail, may

be performed at this point. For the purpose of'holding the pail securelyin station 63when it is upraised by the positioning member, a stationarydisc 260 is provided mounted upon a plunger 261 which is telescoped intoa bushing-262'. A coil spring 263'interposed between the bushing and thedisc biases the disc downwardly.

Positioning of pail and ears in welding station Means are providedwithin the welding station 64"for accurately positioning bail ears onopposite sides ofthe oriented pail in position to be acted upon by thewelding guns. Prior to describing the ear positioner, consideration maybe given to the means employed for positioning the pail at a properheight. It is one of the features of the illustrative welding systemthat a separate adjustable positioner is provided in the welding stationto enable variation in the height of the car on the pail and asnecessary to avoid reinforcing beads which may be formed'in the wall ofthe pail. Thus, there is provided, as shown in FIG. 5, a verticalpositioning memher 230 which is mounted for vertical movement onvertical ways 281, 282.

A linkage connects the positioning member 280 to the rocker shaft sothat the movement is coordinated and timed with the movement of thetransfer member 70 and positionin'gmernber 10% previously discussed.This linkage in the present instance includes an arm 283 which issecured to the rocker shaft and which is connected to a bell crank 284having a pivot point 285. A second bell crank 286 has a pivot point 237.Means are provided for varying the effective point of connection betweenthe bell cranks 284, 286. In the present instance this is accomplishedby providing a pivot block 288' in the bell crank 286 with an adjustingscrew 289 for adjusting the throw. ables the positioning member 280' toreach any desired eight at the top of the stroke at which point the earsare atiixed;

For the purpose of holding the drum in position in the Welding station,a disc 290 is mounted upon a shaft 291 slidable in the bushing 292, withthe disc being urged downwardly by means of a coil spring 293'surrounding the shaft. 7

Attention will next be given means for depositing an car on each side ofthe pail timed with the advancement of a pail into the welding station.orienting the ears to face the pail, an orienting device 300 is employedhaving downwardly extending chutes 301, 302 respectively. The orientingdevice does not per se form apart of the present invention and it willbe understood that any suitable orienting arrangement, taken from theprior art, may be employed. Moreover, it will be understood thatconveyor means, for example, of the magnetic belt type, may be providedfor elevating the cars from a bulk source to the orienting device 300.Since the feeding arrangements for the two sides of the pail areidentical, attention may be focused upon that visible at the front ofthe machine. At the lower end of the chute 301 is an escapement 310. Theescapement includes a rocking assembly 311 which is oscillated about apivot 312 by means of a link 313 which is connected to solenoidoperators having input coils 314, 314a. For the purpose of accepting anear from the chute 301 at one end of the stroke and for releasing theear at the other end of the stroke, the escapement member 311 includes afiat leaf spring member 317 having a retaining forward edge 318 mountinga cam follower 319 which cooperates with a stationary cam surface 320 Itwill be apparent that with an ear in the position shown in FIG. 6,clockwise rotation of the escapement will cause the cam follower 319 toapproach the cam 320. When engagement takes place, the cam follower iscammed laterally bending the leaf spring 317 so that the edge 318thereof moves out of the way of the ear, whereupon the ear is permittedto fall through a final vertical slide chute 321. Preferably, the sideof the chute 321 are grooved as indicated It will be apparent that theadjustment 289 en-' For the purpose of at 322 so that the ear ispositively guided in its downward movement. The escapement memberincludes an obstructing face indicated at 325 which holds the nextsucceeding ear, indicated by the dot-dash outline, in the position shownuntil the escapement member has fully retracted, whereupon such eardrops into place in readiness for a subsequent discharge cycle. Controlcircuits for energizing the coils 314, 314a of the solenoid will bediscussed in detail in connection with consideration of FIG. 21. It willsuflice for the present to say that reload of the escapement is disabledwhenever the pail is not in proper orientation, i.e., whenever theswitch 256 is actuated indicating that the positional tolerance has beenexceeded.

In the exemplary apparatus means providing a supporting table areprovided for catching the car as is descends down the final chute 321and for supporting the ear at the proper height in horizontal position.Moreover, means including a tapered positioning pin are provided forentering the bail opening and for precise final centering of the carjust prior to engagement by the welding electrodes. Thus, there' isprovided at the Welding station a locating table 330 and a taperedcentering pin 331 with means for bringing them into operationsequentially. Sequential operation is brought about by mounting both ofthe elements on a vertically arranged positioning arm 332 having anupper horizontal axis 333 and by providing a resilient mounting to holdthe table in projecting position. Thus, in the present instance thetable 330 has a mounting block 334 which is slidable on a rearwardlyprojecting rod 335 and which is biased to forward position by a spring336. Accordingly, as the centering arm 332 is swung forwardly, i.e., inthe direction of the pail, the table 330 first engages the wall of thepail to provide a positive stop for the advancing bail ear 34. Uponcontinued inward movement of the arm 332, the tapered centering pin 331enters central opening 36 in the ear so that the ear centers itself withrespect to the pin. Since the pail is rotationally oriented with respectto the machine, and since the ear is thereby positioned with respect tothe machine while being held horizontal, it will be apparent thatprecise location of the car on the side of the pail is assured. Meansare provided for swinging the positioning arm timed with the movement ofthe welding guns as covered in the following section.

Construction and actuation of welding guns In the welding station twoseparate welding gun assemblies 350 are provided, one at the front ofthe machine and one at the back of each consisting of two sets ofelectrodes so that both of the ears are welded simultaneously. Since thetwo assemblies are substantially identical, detailed attention may begiven to the assembly at the front of the machine. In accordance withthe present invention, the piece to be welded is provided with a sharpprojection at each point of welding for penetration of a protective, orinsulating coating on the pair, and means are provided for advancing thewelding electrodes by positive mechanical action to develop a forcesufiicient to cause penetration of the coating by the projectionfollowed by substantial collapse of the projection before weldingcurrent is applied, thereby to produce a sound weld free of any tendencytoward flashing, or burning away of the projections. To make the twowelds, the welding assembly 350 has two welding guns 351, 352. The firstgun 351 is mounted on a bracket 353 secured to a frame 354. The bracketis of C-shape having guide portions 355, 356. Mounted for slidingmovement in the bracket is a cylindrical electrode carrier 357 mountinga rod 358 which projects forwardly, carrying an electrode 359 having aterminal 360.

The second gun 352 is mounted in a bracket 363 having ends 365, 366 forthe slidable mounting of a cylindrical electrode carrier 370 having arod 368 terminating in an electrode 369 and terminal 370a. The returncircuit for the electrodes 369, is completed through a relativelystationary electrode 371.

Means are provided in the present construction for cyclically retractingthe electrode 371 downwardly so that it is out of the way of a pailbeing advanced into the welding station and for then moving theelectrode upwardly to a position within the pail after the pail comes torest. In the present instance this is accomplished by mounting thereturn electrode 371 at the end of an electrode arm 375 which is pivotedto the base 354 upon a shaft 376. Extending downwardly from the arm 375is a drop link 376a which is connected to an arm 377 mounted on therocker shaft 120. It will be apparent that when the rocker shaft rocksduring the transfer portion of the cycle, the arm 375 and its electrode371 are swung downwardly clear of the advancing pail and swung upwardlyagain to the position shown When the pail is clamped in the weldingstation.

7 Means including a stiff preloaded spring are provided for positivelyadvancing the welding electrodes and for maintaining the electrodesclamped securely against the ear prior to, and during, the weldingcycle. Thus, referring to FIG. 14, a spring 380 is mounted within thecylindrical carrier 357 surrounding the rod 358. The rod is formed withan enlargement 381 which is normally seated in a recess 382 formed inthe forward end of the cylinder. The spring is compressed at its rearend by a preload adjusting member 385 which is in the form of a bushingthreaded into the end of the cylinder 357, the bushing having a centralbore 386 for clearing the rod 358. It will be apparent, then, that whenthe bushing 385 is screwed into the end of the cylinder, the spring iscompressed to exert a substantial force, which in a practical case maybe on the order of 350 lbs., against the enlargement 381 on the rod.Thus, when the carrier cylinder 357 is advanced forwardly, and theelectrode strikes the workpiece, there is an immediate buildup of forceagainst the workpiece until the force is suflicient to lift the rod fromits seat 382 against the force exerted by the preloading spring. Aspring pressure of at least the value of the preload then continues tobe exerted against the seat workpiece during the remainder of thewelding cycle. It will be understood that an identical preloaded springarrangement is included within the cylinder 367 associated with thecompanion welding electrode.

For the purpose of advancing the electrode carriers with positivemechanical action for complete overcoming of inertial effects, ascontrasted with the non-positive action of an air cylinder or the like,a driving linkage is employed including a cam and over-driven camfollower driven by the cam shaft 83. Thus, there are mounted on theshaft 83 a pair of cams 391, 393 which cooperate with a cam followerlever 393a to reciprocate a vertical link 394. The latter drives a bellcrank 395 which is mounted for rocking about a shaft 396. The upwardlyextending portion 397 of the bell crank is pinned to the reciprocatingbar 398. For the purpose of insuring substantially pure reciprocation, asecond vertical link 399 is provided which is pivoted on the shaft 326and which serves to complete a parallelogram. In short, rotation of thecame shaft causes the bar 398 to reciprocate backwardly and forwardly.For the purpose of coupling the reciprocating bar to the electrodemounting cylinders, short links 401, 402 are provided in the form ofturnbuckles which are secured at their forward ends to the bar 398 andwhich are connected at their rear ends to clamps 403, 404 respectivelywhich grippingly encircle the two cylinders. The walls of the cylindersmay be grooved as necessary to accommodate or clear the rear ends of thelinks 401, 402.

As best shown by. reference to FIGS. 17 and 18, gates are provided atthe lower end of the chute 321 for the purpose of guiding an ear droppedby the escapement 310, to welding position together with means formoving the gates out of the way of the advancing electrodes 359,

1 l 369. Thus, two gates 411, 412 are provided having longitudinalgrooves 413, 414- which serve to guide the ends,

or welding tabs, on the ear 34. The grooves 413, 414,

with the gates in normal position, are alined with corre spondinggrooves in the chute 321. To mount the gates for outward swingingmovement they are pivoted upon pins 415, 416 respectively. The gate 411is held closed by a coil spring 421. The spring is mountedon a push rod422 which is guided at its'upper end at 423 and which is pinned, at itslower end, to an arm 4-24 on the gate. The normal or closed position ofthe gate is defined by engagement of stop surfaces at 4-25. Acorresponding spring 431 on a rod 432 serves the same purposefor thegate 412. In order to swing the gate apart a cam and cam follower areinterposed between the gate and the centering arm 332 which carries thecentering pin 331'previously discussed. Thus, there is provided on thecentering arm a transversely positioned cam plate 440 engaging camrollers 441, 442 mounted on the gates 411, 412 respectively.

Attention may next be given to the means employed for swinging thecentering arm 332 to insure that it is timed with respect to theadvancement of the electrodes. As shown, such arm is coupled to thereciprocating oar 358 which serves to drive the electrode supportingcylinders. Thus, connected to the bar 398 and extending upwardlytherefrom is a link 45%) which is pivoted at its upper end 451 on aframe bracket 452. For interconnecting the arm 332 and the link 45%) apush rod 453 is provided which is pinned to the arm at its forward end454. The connection is made resilient by coil spring 455 surrounding therod and which engages a slidable collar 456 pinned to the center of thelink 4519. It will, therefore, be apparent that when the bar 398 ismoved forwardly, pressure is exerted by the link 45d upon the spring 455to move the push rod 453 in the forward direction so that the pail isengaged by the table, the ear is engaged by the centering pin and thegates are spread apart just ahead of the advancing electrodes.

Switches 457, 453 actuated by a carri surface 459 at the forward end ofthe push rod are operated depending upon whether the push rod goes toofar or not far enough. The switch 457 thus signals the absence of an earin the welding position while the switch 458 signals improperpositioning, the welding guns being disabled in either event as will bediscussed in connection with the control circuitry.

Ear checking arrangement Peeler means are provided in the illustrativeapparatus for checking the presence of ears on the pail upon transfer ofthe pail from the welding station. More specifically, feeler arms arepivoted to the frame in the checking station 65 and moved inwardlytoward the pail to engage the ears when the pail is raised by thepositioning member Referring to FIGS. 19 and 20, the feeler armarrangement at the front and rear sides of the machine is shown indetail and it will be understood that the following description isapplicable to both. Thus, the arm 470 is pivoted at 471 to the frame ofthe machine. At its upper end the arm carries a pivoted finger 4-72having an ear engaging tip 473. For the purpose of adjusting thevertical position of the feeler member, the arm has two relativelyslidable portions including a carrier 474 and with the relative positionbeing adjustable by a control knob 475 which engages a nut 476 on thecarrier. For the purpose of biasing the feeler member 472, a spring isprovided, with the spring force being adjustable by means of a knob 473.Relative rocking movement between the feeler member and the arm when anear is engaged is utilized to control a switch @230 as will be coveredin connection with a discussion of the control diagram, FIG. 21.

For the purpose of rocking the arm forwardly to place the feeler memberin the path of upward movement of the pail, a cam 481 is provided on theshaft 120 engaged by a cam follower 482, which is pinned to the lowerend of the carrier portion 474 of the arm.

the feeler member 472 accompanied by actuation of the switch 48% Thepressure exerted by the spring 477 is sufficient so that there isinsurance that any ear which passes the checking step will have astrength which is adequate for all normal usage of the resulting pailalthough the checking mechanism does not develop the full strength ofthe weld.

In order to hold the pail steady as it is acted upon by the feeler arms,a disc 4% is provided which is similar to that in the welding station.The disc is carried on a vertical shaft 491 slidably received in abushing 492 and urged in a downward direction by a coil spring 493 Thelast station 66 is an idle station which may be employed to perform anadded operation on the pails thereby to increase the versatility of themachine. a clamping disc Still on a shaft Sill slidable in a bushing 5&2and with the disc being biased downwardly by a spring 5%. When the pailleaves the station 66 it is moved by the transfer member onto theconveyor 150. A reciprocating type pusher mechanism may be employed tomove pails laterally from the conveyor for reject purposes.

In the above discussion, it has been assumed that the mechanism has beenadjusted for one size of pail. Means are provided for accommodating themachine to pails of different heights by raising or lowering thesuperstructure 55. Conveniently, this may be accomplished by a heightadjusting drive including a motor 510 having an angular drive connection511 for rotating shafts 512, 513 which extend along the top of themachine. Such shafts rotate worm driven nuts 514, 515 which cooperatewith threaded jack screws 516, 517. It will be apparent, then, thatsimply rotating the motor in one direction or the other thesuperstructure may be moved upwardly and downwardly along way surfaces.As previously disclosed this does not effect the adjustment of therotary orienting mechanism because of the double parallelogram linkageemployed in the latter.

Integrated control circuit While the sequence of operation of thewelding machine will be understood in the general way from the precedingdiscussion of the structure, the various functions are integrated in anovel fashion under the control of a control circuit which is set forthin simplified form in MG. 21. To insure proper timing of the variousfunctions we prefer to use a multiple section cam switch which iscoupled to the cam shaft 33 at a 1:1 speed ratio. The cam switch isindicated generally in FIG. 2 by the numeral 53% and it may beconveniently driven by a suitable angular drive connection from the samechain 143 which serves to drive the conveyor 140. The various sectionsof the cam switch have been indicated in FIG. 21 at 525L539 inclusive.

Turning to FIG. 21, lines 551, 552 will be understood to be connected tothe regular commercial supply line. In series with the main drive motor59 is a switch or control 553. In series with the orienting motor 181 isa suitable switch 554. The motor 555 which drives the hoppers has acontrol switch 556. Finally, the adjusting motor 515 for adjustingheight of the structure, which is ,of the reversible type, has up anddown switches 557,

558. It will be understood that during the normal operation, controlswitches 553, S54 and 556 will be closed and the switches 557, 558 willbe open so that the adjusting motor remains at a constant adjustment.

As the cam shaft 83 rotates to drive the transfer and Thus, in a typicalsequence it will be understood that the arm is rocked radially inwardtoward the pail so that the tip 473 is in the path of movement of theear.

movement of the pail by the positioning member causes the spring to becompressed, with rocking movement of' Continued upward It includespositioning members 70, 100, pails will be transferred simultaneouslyinto all of the stations. Directing attention to the pail in the firstorienting station 61, the sections 531, 532 of the cam switch areclosed, thereby closing the circuit to a course orient relay 560 havingcontacts 561, 562, 563. The contacts 561 are normally open and connectedin series with the clutch 175 while the contacts 562 are normally closedand connected in series with the brake 176. The contacts 563 which arenormally open, serve the purpose of sealing in contacts and areconnected in series with the switch 194 controlled by the star wheel190. Because of the scaling in contacts, the relay 560 remains closed,energizing the clutch 175 to rotate the pail engaged by the disc 170.When the seam of the pail arrives, tripping the star Wheel 190, theswitch 194 momentarily opens, dropping out the relay. This deenergizesthe clutch so that the seal is stopped with the seam thereonapproximately oriented in desired position.

Directing attention next to the pail in the fine orient station 62,there is provided a relay 570 having contacts 571, 572 and 573. Theswitch 255 of the detector 250 is connected in series with the contacts573 which perform a scaling function. After a pail has been moved intothe orienting station 62, the section 533 of the cam switch is closed,picking up the relay 570 and energizing the, clutch 175a. This producesrotation of the disc 170a at slow speed because of the step-down geardrive shown in FIG. 8. When the slow speed detector engages the seam ofthe pail, the switch 255 is opened dropping out the relay 570 whichdeclutches the drive and energizes the brake 17612 to locate the pail ina precisely oriented position.

For the purpose of dropping ears into the welding station, theescapement 310 shown in FIG. 6 is, as stated, operated by two solenoids314, 314a under the control of the sections 534, 535 of the cam switch.The timing of the cam switches is such that the two solenoids arenormally operated in sequence. Thus, the solenoid 314 will be operatedto drop an ear, but before the next ear can be dropped the escapementmust be reset by operat ing reload solenoid 314a. In accordance with oneof the detailed features of the invention, the overtravel switch 256,which is under the control of the slow speed detector 250, is connectedin series with the reload solenoid 314a. Consequently, the reloadsolenoid performs a memory function, i.e., no reloading of theescapement takes place to enable dropping of an ear in the succeedingcycle. To summarize, any overtravel of the pail in the final orientingstation opens the switch 256 to'prevent reloading of the escapement;consequently, when the misoriented pail reaches the next, or weldingstation, no ears will be dropped on either side of the pail forengagement by the gauge pins 331 to enable operation of the weldcontroller. The weld controller has been indicated at 580.

Turning attention to the weld controller circuit, it will be noted thatthe switches 458, which are normally closed, and the switches 457, whichare normally open, associated with the gauge pins 331, are all connectedin series with the section 535 of the cam switch. Thus, the cam switch,when the remainder of the circuit is completed, normally acts toenergize the weld controller 580 to initiate the welding. The nature ofthe weld controller, and the particular sequence of force and curentwhich is employed in the present invention will be covered inthefollowing section.

However, as far as the gauge pin switches are concerned, the absence ofany ears in the welding station causes the pins to overtravel, therebyopening the normally closed switches 458 and preventing a circuit frombeing completed to the weld controller. In short, when no ear-drop takesplace to a mis-oriented pail, the weld controller is effectivelydisabled so that no-weld occurs.

In the illustrative apparatus, aspects of the means are provided forcounting succesive pails found to lack ears in the checking station 65and for shutting down the machine, or for notifying the machineoperator, when the number of such successive pails reaches apredetermined total. It will be understood from the above that the lackof ears on a pail in the checking station will most commonly be due tothe fact that such pail was not properly oriented thereby disablingear-drop reload solenoid 314a. Thus, it is presumed that when a group ofsuccessive pails are found to be without ears, the machine should beshut down until appropriate adjustment may be made in the finalorienting station. To accomplish automatic shut down there is providedin the present device an ear test relay 585 having normally opencontacts 586 and normally closed contacts 587. The relay 585 isconnected in series with section 537 of the cam switch and the ear testswitches 480 in the ear checking station at opposite sides of themachine. The contacts 586, 587 are used to control a counter 590 havinga count line 591 and reset line 592. Connected in series with the resetline is section 538 of the cam switch.

The ear checking switches 480 are normally closed. Thus, in the eventthat a pail in the checking station lacks ears, switches 480 will remainclosed with the result that cycling of the cam switch section 537applies an impulse to the relay 585, picking up the relay to causeclosure of the normally open contacts 586 to register a count in thecounting circuit. To store the count, i.e., to prevent resetting of acounter upon deenergization of the relay 585, a latching relay 595 isemployed having a latch 596 which engages a cooperating latch member 597on the plunger of the relay 585. Thus, the relay 585 is, temporarily,prevented from dropping out to the point of closing the contact 587.

If the next pail to enter the checking station 65 is also without ears,the above operation will be repeated, i.e. the relay 585 will beenergized to close the contacts 586, so that a second count isregistered in the counter. The counter may be a commercially availabledesign so that upon reaching a set count, output contacts are operated.The output contacts, in the present instance indicated at 598, are inthe form of normally closed contacts connected in series with thecontrol circuit for the main motor 90. Thus, when the desired count ofnon-eared pails is reached, which may be five in a practical case, themain driving motor is shut off, bringing the machine to a halt andclearly signifying to the operator that an adjustment should be madebefore operation is continued.

However, when an eared pail is detected prior to the set count,resetting is effected by section 539 of the cam switch. Since the latteris in series with the latch relay 595, the latch 596 is withdrawn andcontacts 587 are closed to apply a reset signal to the line 592 whichfeeds the counter.

In order to prevent the latching relay from producing unwanted reset,the on time of the cam section 539 is made very short and is adjusted tofall within the on time of the cam section 537. Thus, when a pailwithout ears is in the checking station, resulting in energization ofthe relay 585, the latching relay 595 will be momentarily energizedduring the time interval that the relay 585 is picked up. Because of theshortness of the time of energization of the latching relay, the latchwill fall back into latching position before the relay 585 becomesde-energized. Briefly stated, while it is true that the latching relay595 is operated once each cycle, it is effective to unlatch the relay585, i.e., to permit it to drop out, only when there is an eared pail inthe checking station, since it is only then that the switches 480 areopened.

While the construction and operation of the counter 590 will be apparentto one skilled in the art from the foregoing description, it will beunderstood that we prefer to employ a counter of type HZA601manufactured by Eagle Signal Co. and described in their Bulletin 725.

For the details of the program of the cam switch, reference is made toFIG. 21a which shows the on time for the switch sections 531-539employed in the case of a practical installation.

F Oreo-current cycle of projection welding through protective coatingWhile. the discussion has been directed toward the structuralaspectsofthe Welding. machine, it-is one of the important aspects of'the invention to provide a specific relationship between the structureand the specific forcecurrent cycle which has been found to enableperfectly reliable Welding through paint, lithographing, or otherprotective coating on thesurface of the pail. As stated above; thepresent invention contemplates that thepainting or lithographing willtake place-While the pail is-still' in the-flat condition, withthesurface being thoroughly covered-so that no bare spots are available formaking electrical contact.

In carrying out the invention we preferably employ a projection which isthe result of a piercing operation so as to produce a tapered relativelysharp edge of limited cross section. A sectional view, taken through theprojection and associatedbase memberlthe wall of the pail) is setforthin FIG. 23A, the scale being greatly enlarged tofacilitateunderstanding. Thus, the'projection indicated at 600, has a relativelysharp edge 6&1. in a practical case, such edge will not be smooth andcontinuous but on the contrary will be ragged or sawtoothed to define anumber of projecting points arranged ina circular locus. In the samefigure the base member has been indicated at 605 and the coating thereonby the layer 606. The projection has a height from the surface of theattachment indicated at Ill; The welding electrodes 369, 371 previouslydiscussed, and which are indicated by the dimension line in the figurepreferably occupy an area, which is substantially greater than thediameter of the projection, the major diameter of the projection beingindicated at d1 and the minor diameter at d2.

In order to better understand the reasons for the effectiveness of thepresent apparatus and procedure in securing a sound weld through aninsulating coating a series of stop motion cross section views have beenprepared as set forth in FIGS. 23a-23b inclusive and which are keyed toa plot of projection height, pressure and current in a typical weldingcycle. The figures are based upon actual observations made in an effortto explain successive occurrences during the cycle.

FIG. 23a shows the initial condition with the electrodes brought intolight contact With the work but with substantially zero force appliedand with the coating not yet penetrated. Upon. slight additionalmovement of the movable electrode, the force applied rises rapidly asindicated at P1. Since the spring is preferably'stiff having apro-stress force of approximately 330 pounds, concentrated upon aprojection diameter d2 of only 0.040 inch, the sharp edge of theprojection is forced through the coating to establish a limited area ofelectrical contact followed immediately by deformation or partial axialcollapse of the projection to the condition shown. in FIG. 23b and withthe projection height being reduced to a value 12. That is, the sharpedge 601 is crushed and tends to spread out in both radial directions,defining a reduced inner diameter :13 and an increased outer diameterd4. The net eifect is to substantially increase the cross sectional areaof the metal at the edge ofthe projection. The initial electricalcontact made between the parts, for example as indicated at 607, ismaintained during the transition and, in the following steps, the areasof electrical contact may even be enlarged depending upon the nature ofthe coating material. It may be emphasized at this point that it is oneof the features of the present invention that advancement of theelectrode 369 and the buildup of force along applied force curve takesplace positively substantially free of the effect of inertia or othertransient effects which characterize air actuators or the like commonlyemployed in welding practice. Thus, the

transition between conditions of contact shown in the stop motion viewsis progressivefrorn the time that the initial electrical-contact is madeto the time that the projection is substantially flattened and freeof-any momentary release or reboundwhich might affect the continuity ofthe electrical circuit.

Asthespring380 in he Welding-gun 351-is picked up, in other Words, asthe central rod 358 isunseated from the seat 382in the gun, the forceexerted by the electrode 369 further increases, reaching a value F2(FIG. 22) accompanied by furtherdeformation ofthe projection,

with the height being reduced to the value 113, the inner diameter beingreduced'to the value d5 and the outer diameter'beingincreased tothe-value d6. The contact areas 6(l7'remain inengagement and-some-of-thecoating material is trapped-as-indicated at 603.

At theend'ofthe forward stroke of the gun actuating bar 398 '(FIG. 14),the throw of which is determined by the cams which drive it, the barremains temporarily stationaryto apply a high sustained force to thewelding electrode having a value indicated at P3 in FIG. 22.Increaseforce to the maximum value further deforms the projection untilit appears as setforth in H6. 23d. Here it will'be noted that the innerdiameter of the projection has been reduced to the point where theprojection is substantially closed. The contact is maintained andenlarged over areas an and pockets of coating material 608become morewell-defined.

It is one of the features of the present invention that application, offull welding current is delayed until after the projection has beensubstantially deformed, that is, substantially flattened out asindicated in FIG. 23c or FIG. 23d. Thus the current is preferably turnedon at point 01', i.e., after a delay'time t1 from the start of thewelding cycle which may be in the order of second. This timing isachieved in the present instance, by the phase of section 536 of the camswitch which is in series with the input to the Welding controller.However, as the discussion proceeds it will'be apparent to one skilledin the art that such delay need not be secured by a timed switch andthat, if desired, the current may be initiated;

by a switch which is responsive to the build-up of the force applied by.the electrode 369 and. spring 38%.

It is a further feature of the present invention that the current, whenapplied, is not applied at full welding value but means are providedwithin the welding controller 580 for causing the current to build upfrom a reduced value 01 or less linearly along a characteristic curve c2to a final value 03. Such build up of curernt in a practical case maytake place over an interval t2, on the order of second in length.Welding controllers capable of such upslope with variable rise time arecommercially available.

Current and force are both thereafter maintain-ed at the values c3, 3,respectively, which may be in the order of 9,000 amperes and 350 pounds,over a further interval t3 which may be on the order of 0.25 second. Theheating which takes place during this time interval produces atemperature which is sufficiently high so that the metal softens andflows under the applied pressure so that complete flattening of theprojection takes place, with loss of identity and with the two pieces ofmetal being united over the area of a welding nugget 610 having an areawhich is substantially greater than the area of the original projection.During this portion of the cycle any entrained coating material isdecomposed and is found not to affect the soundness of the weld.

It is found that by using the above procedure, flashing, i.e., theburning away of the projection is completely eliminated and that eachweld is sound and homogeneous notwithstanding the insulating paint orother coating. Observations show that the elimination of flashing is duein part to the deformation of the thin tapering edge of the projectionfrom the thin initial cross section to substantially thicker crosssection before the application of current without interrupting thecontinuity of the contact originally made and with substantial increasein the thermal coupling between the projection and the relativelymassive pieces of metal lying on the opposite sides of the projection.Because of the increase in cross section and the close thermal couplingexcess localized heat is promptly conducted away so that there is nopossibility of temperature build-up in the projection to the level atwhich burning or flashing away may occur. Localized build-up of heat inthe projection is also minimized by the fact that the electrodes, bothmovable and fixed, constitute an efficient heat sink.

The continuous maintenance of electrical contact from the moment ofinitial contact by the points of the projection is also believed to be acontributing factor. As stated, such contact is maintained by reason ofthe fact that the electrodes are advanced positively and progressivelywithout being affected by inertia effects or rebound. Moreover, use of apierced projection, as in the preferred embodiment of the invention,tends to produce a scraping action as the projection is deformed, with"part of the edge scraping inwardly to reduce a minimum diameter of theprojection and the remainder scraping outwardly to increase the maximumdiameter. Where such a projection is used and where the parts are putthrough a pressure cycle without application of the welding current, itis found that the insulating coating tends to be substantially clearedfrom a small but rather well defined annular area. This scraping actionis, however, to be distinguished from the scraping which might occur dueto bodily deformation of the ear being attached. In the prestgntprocedure deformation is limited to the projection 1tse After thewelding current has been applied the additional time t3 the current iscut off as shown in FIG. 21 but force continues to be applied for anadditional time interval t4 to permit the weld to cool and remain intactwhen the force on the welding electrodes is released.

It is particularly noteworthy that all of the above occurs within anextremely short period of time, on the order of one-half second and itis, indeed, one of the features of the present machine that in spite ofthe sequential action production rates are obtainable which arecomparable to or even higher than where conventional bare metal weldingtechniques are employed.

While a pierced projection has been described as the preferredembodiment, it will be understood that other specific shapes ofprojections may be employed having a relatively sharp edge forpenetrating a coating, where the edge is either continuous or localizedin the form of a point and where deformation of the edge occurs toincrease the cross section and hence the thermal coupling uponapplication of force and prior to the application of the full weldingcurrent.

We claim as our invention:

1. In a projection welding set-up for a base member in the form of asheet of metal having an insulating coating and an attachment formed ofa substantially flat piece of sheet metal intended to be secured to thebase member face to face having a projection on its face with a sharppresented edge capable of penetrating the insulating coating andprogressively collapsing as force is applied at right angles thereto,the combination comprising first and second welding electrodes arrangedopposite one another and having substantially flat faces with an areasubstantially larger than the area of said projection, at least one ofsaid electrodes being movable toward the other, force transmitting meansfor positively advancing the movable electrode into contact with thework so that the base member and attachment are bottomed together on theprojection, and a stifl. preloaded spring interposed in the forcetransmitting means so that the force exerted by the electrodes isincreased from an initial value to a sustained higher value so that saidprojection is axially crushed thereby causing penetration of the coatingand thereafter substantially complete axial collapse of the projection,a

source of welding current connected to the electrodes, means fordelaying the turning on of the welding current until the force reaches avalue which corresponds to the substantially complete collapsing of theprojection, means for varying the current gradually from a low value toa sustained high value so that the heating of the projection resultingfrom the current flow takes place gradually with the formation of awelding nugget having an area substantially greater than the area of theprojection, and means for causing the current to be turned ofi and themovable electrode subsequently retracted for removal of the basememberand attachment from between the electrodes.

2. In a projection welding set-up for a base member in the form of asheet of metal having an insulating coating and an attachment formed ofa substantially flat piece of sheet metal intended to be secured to thebase member face to face having a projection on its face with a sharppresented edge capable of penetrating the insulating coating andprogressively collapsing as force is applied at right angles thereto,the combination comprising first and second welding electrodes arrangedopposite one another and having substantially fiat faces with an areasubstantially larger than the area of said projection, at least one ofsaid electrodes being movable toward the other, force transmitting meansfor advancing the movable electrode so that the base member andattachment are bottomed together on the projection, a resilient memberinterposed in the force transmitting means so that the force exerted bythe electrodes is increased from an initial value to a sustained highervalue so that said projection is axially crushed thereby causingpenetration of the coating and thereafter substantially complete axialcollapse of the projection, a source of welding current connected to theelectrodes, means for delaying the turning on of the welding currentuntil the force reaches a value which corresponds to substantialcollapsing of the projection, means for varying the current graduallyfrom zero value so that the initial heating of the collapsed projectionresulting from the current flow takes place gradually followed by flowof a sustained high current suflicing to insure the formation of awelding nugget having an area substantially greater than the area of theprojection, and means for causing the current to be turned off and themovable electrode subsequently retracted for removal of the base memberand attachment from between the electrodes.

3. In a projection welding set-up for a base member in the form of asheet of metal having an insulating coating and an attachment formed ofa substantially fiat piece of sheet metal intended to be secured to bebase member having a projection with a sharp presented edge capable ofpenetrating the insulating coating and progressively collapsing as forceis applied at right angles thereto, the combination comprising first andsecond welding electrodes arranged opposite one another and havingsubstantially flat faces with an area substantially larger than the areaof said projection and providing an efficient heat sink, at least one ofsaid electrodes being movable toward the other, a motor, mechanicalmeans directly coupled to the motor for advancing the movable electrodeinto contact with the work so that the base member and attachment arebottomed together on the projection, and a stiff preloaded spring beinginterposed in the force transmitting means so that the force exerted bythe electrodes is increased from an initial value to a sustained highervalue as the spring is compressed, the said higher value beingsufficiently high so that the projection is axially crushed and (a)first penetrates the insulating coating over a limited control area and(b) then flattens out in good heat transferring relation to the basemember and attachment, a source of welding current connected to theelectrodes, means for turning on the welding current automatically afterthe projection has been flattened out at a value which is sufiicientlylow so that the excess of heat localized in the projection is kept to alevel which may be transferred to the base member and attachment foravoidance of flashing and with the current thereafter in creased to alevel which is sufiiciently high as to insure formation of a weldingnugget having an area substantially greater than the area of theprojection, and means for causing the current to be turned off and themovable electrode subsequently retracted for removal of the weldedmember and attachment from between the electrodes.

4. In a projection welding set-up for a base member in the form of asheet of metal having an insulating coating and an attachment formed ofa substantially flat piece of sheet metal intended to be secured to thebase member having a projection with a sharp presented edge capable ofpenetrating the insulating coating and progressively collapsing as forceis applied at right angles thereto, the combination comprising first andsecond welding electrodes arranged opposite one another havingsubstantially flat faces with an area substantially larger than the areaof said projection and providing an efiicient heat sink, at least one ofsaid electrodes being movable toward the other, means for advancing themovable electrode free of rebound upon striking the work and formaintaining a force between the base member and attachment which issufficiently high so that the projection is axially crushed and (a)first penetrates the insulating coating over a limited contact area and(b) then flattens out in good heat transferring relation to the basemember and attachment, a source of welding current connected to theelectrodes, means for applying the welding current gradually and at aninitial value which is sufificiently low so that the heat localized inthe projection by reason of the limited contact area is neverthelesskept to a level which permits transfer of excess heat to the base memberand attachment thereby to avoid flashing away of the projection and withthe current thereafter increased to a level which is sufficiently highto insure formation of a welding nugget having an area substantiallygreater than the area of the projection, and means for causing thecurrent to be turned off and the movable electrode subsequentlyretracted for removal of the welded member and attachment from betweenthe electrodes.

5. In a projection welding set-up for a base member in the form of asheet of metal having an insulating coating and an attachment formed ofa substantially flat piece of sheet metal intended to be secured to thebase member having a projection with a sharp presented edge capable ofpenetrating the insulating coating and progressively collapsing as forceis applied at right angles thereto, the combination comprising first andsecond welding electrodes arranged opposite one another havingsubstantially flat faces with an area substantially larger than the areaof said projection and providing an efficient heat sink, at least one ofsaid electrodes being movable toward the other, means for advancing themovable electrode with positive motion free of inertial efi'ects and formaintaining a force between the base member and attachment which issufiiciently high so that the projection is axially crushed and (a)first penetrates the insulat ng coating over a limited contact area and(b) then is flattened out in good heat transferring relation to the basemember and attachment while maintaining the electrical contact, a sourceof welding current connected to the electrodes, means for applying thewelding current at an initial value which is sufiiciently low so thatthe heat localized in the projection by reason of the limited contactarea is kept to a level which permits transfer of excess heat to thebase member and attachment thereby to keep the temperature below thepoint at which the projection will be flashed away and with the currentbeing thereafter sustained at a level which is sufiiciently high toinsure formation of a welding nugget having an area substantiallygreater than the area of the projection, and means for causing thecurrent to be turned off and the movable electrode subsequentlyretracted for removal of the welded member and attachment from betweentheelectrodes.

6. In a projection welding set-up for a base member in the form of asheet of metal having an insulating coating and an attachment formed ofa piece of metal intended to be secured to the base member having aprojection with a thin tapered edge of limited cross section capable ofpenetrating the insulating coating and progressively collapsing as forceis applied at right angles thereto, the combination comprising first andsecond welding electrodes arranged opposite to one another havingsubstantially flat faces with an area substantially larger than the areaof said projection, at least one of said electrodes being movable towardthe other, means for positively controlling the advancement of themovable electrode so that movement takes place positively and free ofinertial effects to bring such electrode into bottoming engagement andfor building up a force between the base member and attachment which issufficiently high so that the projection is axially crushed whereby theedge of the projection first penetrates the insulating coating over alimited electrical contact area and then deforms in both radialdirections to provide a substantial increase in cross sectional areawhile maintaining the electrical contact, a source of welding currentconnected to the electrodes, timed control means for applying thewelding current gradually after substantial deformation of theprojection has taken place with the current being suflicient to heat theprojection to facilitate the final deformation thereof and to effectdecomposition of any coating material trapped by the deformed projectionand with the current being thereafter sustained at a level which issufiiciently high to insure formation of a welding nugget having an areasubstantially greater than the area of the projection, and means forcausing the current to be turned off and the movable electrodesubsequently retracted for removal of the welding member and attachmentfrom between the electrodes.

7. In a method of welding to a base member, in the form of a sheet ofmetal having an insulating coating, an attachment formed of a piece ofmetal having a projection with a thin tapered edge of limited crosssection capable of penetrating the insulating coating and progressivelycollapsing as force is applied between the attachment and base member,the steps of positioning on opposite sides of the attachment and basemember, the steps of positioning on opposite sides of the attachment andbase member first and second opposed welding electrodes havesubstantially fiat surfaces with an area substantially larger than thearea of said projection, positively advancing at least one of theelectrodes to bring the electrodes into bottoming engagement with thebase member and attachment, building up a force therebetween which issufi'iciently high so as to axially crush the projection thereby causingthe latter to first penetrate the insulating coating over a limitedelectrical contact area and then deform to provide a substantialincrease in the cross sectional area of the edge of the projection whilemaintaining electrical contact with the base member, applying current tothe electrode after the deformation has progressed to the point ofsubstantial increase in cross sectional area which is below the flashinglevel but high enough to soften the projection for progessive axialcollapsing action in the face of the applied force, increasing thecurrent while sustaining the applied force so that the projection issubstantially flattened, thereafter sustaining the current at a levelwhich is SlLlClfiIllllY high to insure formation of a welding nuggethaving an area substantially greater in the area of the projection, andturning off the current and retracting the electrodes for removal of thecombined base member and attachment.

UNITED 21 STATES PATENTS V Blevins et a1. Soelch 198-432 Bowker 19,8-232Von Hofe et a1. 1 9833 Goldworthy 2 19-93 Hofi 340 -259 Hansen 198-33 2Hall l 219-93 Barrett et a1 340-259 Emnions et a1. 219 -93 Webb 21969 XHamcister et a1. 198--19 Opperthauser 198--19 RICHARD M. WOOD, PrimaryExaminer.

1. IN A PROJECTION WELDING SET-UP FOR A BASE MEMBER IN THE FORM OF ASHEET OF METAL HAVING AN INSULATING COATING AND AN ATTACHMENT FORMED OFA SUBSTANTIALLY FLAT PIECE OF SHEET METAL INTENDED TO BE SECURED TO THEBASE MEMBER FACE TO FACE HAVING A PROJECTION ON ITS FACE WITH A SHARPPRESENTED EDGE CAPABLE OF PENETRATING THE INSULATING COATING ANDPROGRESSIVELY COLLAPSING AS FORCE IS APPLIED AT RIGHT ANGLES THERETO,THE COMBINATION COMPRISING FIRST AND SECOND WELDING ELECTRODES ARRANGEDOPPOSITE ONE ANOTHER AND HAVING SUBSTANTIALLY FLAT FACES WITH AN AREASUBSTANTIALLY LARGER THAN THE AREA OF SAID PROJECTION, AT LEAST ONE OFSAID ELECTRODES BEING MOVABLE TOWARD THE OTHER, FORCE TRANSMITTING MEANSFOR POSITIVELY ADVANCING THE MOVABLE ELECTRODE INTO CONTACT WITH THEWORK SO THAT THE BASE MEMBER AND ATTACHMENT ARE BOTTOMED TOGETHER ON THEPROJECTION, AND A STIFF PRELOADED SPRING INTERPOSED IN THE FORCETRANSMITTING MEANS SO THAT THE FORCE EXERTED BY THE ELECTRODES ININCREASED FROM AN INITIAL VALUE TO A SUSTAINED HIGHER VALUE SO THAT SAIDPROJECTION IS AXIALLY CRUSHED THEREBY CAUSING PENETRATION OF THE COATINGAND THEREAFTER SUBSTANTIALLY COMPLETE AXIAL COLLAPSE OF THE PROJECTION,A SOURCE OF WELDING CURRENT CONNECTED TO THE ELECTRODES, MEANS FORDELAYING THE TURNING ON OF THE WELDING CURRENT UNTIL THE FORCE REACHES AVALUE WHICH CORRESPONDS TO THE SUBSTANTIALLY COMPLETE COLLAPSING OF THEPROJECTION, MEANS FOR VARYING THE CURRENT GRADUALLY FROM A LOW VALUE TOA SUSTAINED HIGH VALUE SO THAT THE HEATING OF THE PROJECTION RESULTINGFROM THE CURRENT FLOW TAKES PLACE GRADUALLY WITH THE FORMATION OF AWELDING NUGGET HAVING AN AREA SUBSTANTIALLY GREATER THAN THE AREA OF THEPROJECTION, AND MEANS FOR CAUSING THE CURRENT TO BE TURNED OFF AND THEMOVABLE ELECTRODE SUBSEQUENTLY RETRACTED FOR REMOVAL OF THE BASE MEMBERAND ATTACHMENT FROM BETWEEN THE ELECTRODES.